A model for the consolidation of warp‐knitted reinforced laminates

Abstract

A model for the consolidation of thermoplastic composites reinforced with a warp‐knitted fabric was developed. The evolution of void content during composite consolidation achieved via film stacking was related to the processing parameters and the material properties. Since the knitting process results in local variations of fiber volume fractions even within a tow, the flow mechanisms are not identical to those occurring in homogeneously dispersed fibers. Two different types of micro‐scale porosities were determined and a unit cell geometry was proposed for modeling. The reduction of the effective pressure due to the gas entrapment was also accounted for. Predictions of the variation of the void content as a function of time, pressure and temperature were compared to experimental data. As a good correlation was found between experiments and predictions, this approach can thus be applied to the consolidation of textile reinforcements in which the tows are locally compressed.

A model for the consolidation of hybrid textiles considering air entrapment, dissolution and diffusion

“…Early consolidation models considered the reinforcing textile as a layer with homogeneous thickness, for example Phillips et al [23], Rozant et al [24] or Jespersen et al [15] who based their model on the work of Michaud et al [25][26][27][28] and Sommer and Mortensen [29]. Klinkmüller et al [30] adopted a similar approach for the consolidation of commingled yarns.…”

“…Others, such as Bernet et al [22] in their model about the consolidation of commingled yarns, introduced a threshold during impregnation after which the air gets entrapped. Rozant et al [24] considered that air was trapped in the tows during the whole process in their model about the consolidation of knits. The dissolution of air was however not considered and it is interesting to notice that in their experimental validation the void content decreases continuously with longer consolidation times while the model predicts a constant value as shown in Fig.…”

Consolidation process model for film stacking glass/PPS laminates

“…Bundle impregnation with a thermoplastic resin has been subject of research in a number of comparable studies: for instance in commingled yarn composites 9,11 and film stacking of knitted fabrics. 15 In general, it is assumed that all fibre bundles undergo impregnation simultaneously and all the bundles have an identical geometry. This assumption allows the fabric to be divided into repetitive elements or unit cells, of e.g.…”

Multi-scale effects in the consolidation of thermoplastic laminates

“…Micro-scale impregnation is therefore assumed to govern the total consolidation time. This assumption is also seen in comparable consolidation analyses, for instance in commingled yarn composites [1,2] and film stacking of knitted fabrics [3]. These researchers investigated bundle impregnation by a Newtonian fluid using Darcy's law under the assumption that the fluid flow and bundle deformation are not coupled.…”